Thor Forums

[FW28z]

From a generic point of view, boiling usually comes from applying too high of a charge to a fully charged battery (i.e. overcharge condition).

The only way I could fathom this occurring is if the two batteries are so mismatched that the charger thinks it needs to apply a high charge while one battery is fully charged and begins to boil while the other battery still needs a charge.

That means the boiling battery might actually be the good battery. Of course, it could have sustained damage due to boiling.

The condition you experienced could occur if the boiling battery became 100% charged long before the other battery did, which could occur in a severe mis-match of batteries.

It is pretty complicated when this happens, as the fully charged battery will be attempting to discharge into the partially discharged battery, and the charger will be trying to charge both batteries.

The problem is, with the batteries paralleled, the charger cannot sense what one battery's charge needs are vs. the other. So who knows what charge rate the charger is applying in this situation?

This is one of the disadvantages of paralleling batteries without any kind of isolation between them - if one goes bad, it can fail the other.